Defending Italian Open champion Francesco Molinari was among six players to shoot a seven-under round of 64 in Milan as the fifth Rolex Series event of the year got under way on Thursday.
Molinari recorded a brilliant 22-under for the tournament to win by a single stroke from Danny Willett a year ago and he is seeking a historic third title, having also triumphed in the 2006 edition.
The 34-year-old made a flying start with birdies at the first and second, but dropped shots at the third and eighth holes left Molinari two-under at the turn.
A flawless back nine featured birdies at four of his last five holes, including a superb chip-and-run at the last, to leave Molinari among the leading pack at his home event.
Kiradech Aphibarnrat went out in the first group of the day and set the low-scoring tone with a bogey-free 64, picking up three birdies in the first four holes and maintaining his fine form throughout the round.
The Thai has not won on the European Tour since 2015 but showed he could be a contender for the Italian crown with a typically aggressive display of strokeplay from the off.
Sweden's Alexander Bjork, Englishman Eddie Pepperell, Jamie Donaldson of Wales and late climber Matt Wallace also hit rounds of 64.
Race to Dubai-leading trio Tommy Fleetwood, Sergio Garcia and Jon Rahm comprised the Italian Open's star group and while the Open de France winner could only record a level-par 72, both Spaniards are in the hunt after fine opening rounds.
Masters champion Garcia, who announced this week that he and his partner are expecting their first child, shot five-under and compatriot Rahm, number five in the world rankings, was a single shot back as the 22-year-old looks to follow up his star-making performance at July's Irish Open with a second Rolex Series success of the year.
British Masters winner Paul Dunne looked in good shape to join the leaders after stringing together four birdies on the spin during his back nine, but a dropped shot at the 16th leaves the Irishman three shots off the pace.
Tyrell Hatton is not faring as well after his victory at the Alfred Dunhill Links Championship last week, however, shooting an uneven round that featured three bogeys in his two-under round of 70.